Method and apparatus for reducing nitrogen dioxide (no2) emissions in a flueless heating appliance

ABSTRACT

An apparatus for reducing nitrogen dioxide emissions in a flueless heating appliance comprises heat-exchanger means suitable for being crossed by the fumes produced by the combustion of a fuel in said heating appliance. A heating appliance without a fume flue comprises burner means supplied with a gaseous fuel, evacuation means for discharging into the outside environment fumes produced by the combustion of said fuel and heat-exchanger means suitable for receiving said fumes from said burner means and sending them to said evacuation means. A method for reducing nitrogen dioxide emissions in a flueless heating appliance, supplied with a gaseous fuel, comprises removing heat in a controlled manner from fumes produced by the combustion of said fuel so as to minimize the conversion of NO into NO2 in said fumes.

The present invention relates to a method and apparatus for reducing nitrogen dioxide emissions in a flueless heating appliance, i.e. a heating appliance in which fumes produced by the combustion of the fuel with which it is supplied are discharged directly into the environment in which the appliance is located.

In this type of heating appliance it is essential for the toxic emissions, in particular CO and NO₂, to be kept as low as possible; it is also essential that the percentage of oxygen in the environment in which the heating appliance is located does not fall below a preset level. This is essential in order to safeguard health of the persons who are in said environment.

Particular attention is paid to minimising NO₂ emissions, which, until now, has not been satisfactorily achieved.

Known flueless heating appliances comprise a gas combustion system generally consisting of a pressure adjuster, a gas valve, a burner, flame ignition and monitoring means and a conduit supplying the gas fuel.

The above system is contained in a body provided with a deflector for channelling the combustion products outside and reducing the temperature of said body by shielding it.

These heating appliances can be provided with different types of burners, for example, convection burners or radiant burners, that are aspirated naturally or with assisted aspiration. The gas valve may be manually controlled or thermostatically controlled with finite or variable heat adjustment that is manually or remotely controlled. These heating appliances generally operate without electric power but can be provided with electric ignition and fans.

Flueless heating appliances are also known inside which pieces of artificial wood are located, said pieces of artificial wood are made of ceramic fibre, cement or a mixture of cement and ceramic fibre and are used to give the illusion of the combustion of pieces of wood. The combustion systems used in this type of heating appliance are substantially the same as those mentioned before.

The prior-art flueless heating appliances, despite the progress made over the last few years, have not yet effectively solved the problem of excessive NO₂ emissions.

The present invention aims to provide a flueless heating appliance, in which the percentage of nitric oxides, in particular NO₂, in the combustion products is extremely low. According to a first aspect of the present invention an apparatus for reducing nitrogen dioxide emissions in a flueless heating appliance is provided, said appliance comprising an appliance body in which burner means are arranged that are fed with a gaseous fuel, supplying means for supplying said burner means with said gaseous fuel, adjusting means for regulating said supplying, ignition means for causing the combustion of said fuel, monitoring means for monitoring said combustion, evacuation means for discharging into the outside environment fumes produced by the combustion of said fuel, characterised in that said apparatus comprises heat-exchanger means suitable for being crossed by said fumes and being placed between said burner means and said evacuation means.

According to a further aspect of the present invention a method for reducing nitrogen dioxide emissions in a flueless heating appliance is provided, comprising supplying said heating appliance with a gaseous fuel, causing the combustion of said gaseous fuel in said heating appliance, sending fumes produced by the combustion of said fuel towards an opening of said heating appliance that communicates with the outside environment in order to discharge said fumes into said outside environment, characterised in that it further comprises removing heat from said fumes before they reach said opening, said removing being carried out in order to minimise the conversion of NO into NO₂ in said fumes during said cooling. Owing to the invention the fumes produced by the combustion of the fuel with which the heating appliance is supplied are progressively and slowly cooled without undergoing sudden cooling, as generally occurs in prior-art appliances and they remain at a relatively high temperature for a sufficiently long time to drastically limit conversion of NO into NO₂ before being discharged into the outside environment through said evacuation means.

Further characteristics and advantages of the present invention will be apparent from the following exemplifying and non-limitative description, and from the attached drawings, in which:

FIG. 1 is a partially interrupted perspective view of a heating appliance incorporating an apparatus according to the invention;

FIG. 2 is a perspective view of an apparatus according to the invention;

FIG. 3 is a transparent perspective view of the apparatus of FIG. 2, associated with a burner;

FIG. 4 is an enlarged detail of the apparatus of FIG. 2;

FIG. 5 is a front view of a construction variation of the apparatus according to the invention;

FIG. 6 is a schematic section taken along a plane VI-VI of FIG. 5.

FIG. 1 shows a heating appliance 1 that comprises a body 2 inside which an apparatus 3 according to the invention is arranged. The body 2 comprises a front wall 4 in which a window 5 is obtained, in a substantially central position, which window enables the inner space 6 of the appliance 1 to communicate with the outside environment around it. In an upper zone of said front wall 4 there is a series of top slits 7 whilst in a lower zone of said front wall 4 there is a series of bottom slits 8.

In a rear wall 21 of the body 2 there is a further series of top slits 22 substantially arranged to face the top slits 7 of the front wall 4.

An apparatus 3 according to the invention is arranged in the inner space 6 of the appliance 1. The apparatus 3 comprises heat-exchanger means 9 defined by a frontal wall 10 and by a rear wall 11, connected together by side walls 12, 13. The side walls 12, 13 are provided with respective bottom appendages 14, 15 supporting burner means 16 that are supplied with a gaseous fuel. Said burner means 16 are preferably burner means suitable for producing a dark-blue Bunsen-type flame.

The burner means 16 are arranged to occlude most of the bottom slits 8, so as to limit the quantity of secondary air that enters from the outside into the inner space 6, in the zone in which the burner means 16 are arranged.

The heat-exchanger means 9 transfer towards the outside environment, mainly through the window 5, part of the heat possessed by the fumes produced by the combustion of said gaseous fuel.

The heat-exchanger means 9 receive the fumes produced by the combustion of said gaseous fuel and discharge them through an evacuation opening 17 towards said top slits 7 through which the fumes reach said outside environment. The opening 17 is located at the top zone of the heat-exchanger means 9 and is preferably provided with choking means 18 suitable for modifying the size of the opening 17 in order to regulate the draught of the heating appliance 1 according to variations in thermal power output.

The dimensions of the heat-exchanger 9 are such that the fumes that go through it cool down slowly without undergoing sudden decreases in temperature, in other words without being subjected to the so-called ‘quenching’ phenomenon, and reach the evacuation opening 17 at a temperature that is lower than the minimum temperature at which the NO can be converted into NO₂. The slow cooling of the fumes drastically reduces the conversion of the NO in said fumes into NO₂, so that the NO₂ content in the fumes, when they are ejected into the outside environment through the evacuation opening 17 and the top slits 7 of the body 2, is extremely low and anyway compatible with the NO₂ levels that are permissible in the emissions from flueless heating appliances, according to current regulations or regulations that are to come into force. The heat-exchanger 9 can be used to effectively control the cooling of the fumes to prevent the phenomenon of ‘quenching’, over a: wide modulation field of the heating appliance, substantially between operation at maximum power, i.e. at nominal power, and operation at minimum power, normally at 50% of nominal power. In the embodiment shown in FIGS. 1 to 4 the front wall 10 and rear wall 11 are made with a series of respective consecutive sections 19, 20 of wall that are tilted alternately on opposite side to constitute a vertical zigzag development.

In this way, the route along which the fumes have to travel to reach the evacuation opening 17 is lengthened and the heat-exchange surface is increased across which the heat contained in the fumes is transmitted to the outside environment before said fumes escape from the evacuation opening 17. This conformation of the heat-exchanger 9 enables the same overall height dimensions-as those of a prior-art heating appliance to be maintained.

Said conformation of the heat-exchanger 9 is simple and conveniently obtained and can be achieved with a minimal number of parts and using manufacturing methods with which manufacturers of shaped sheet metal and fitters are thoroughly familiar.

The geometrical configuration of the heat-exchanger 9 shown is just one of the many different types of geometrical configuration that are possible. The geometrical configuration of the heat-exchanger 9 is chosen according to the criterion of allowing transmission of the heat from the fumes towards the outside environment to be achieved, during the interval of time during which the fumes cross the heat-exchanger 9, which enables slow and progressive cooling of the fumes that is suitable for avoiding the phenomenon of quenching and lowers the temperature of the fumes below the minimum temperature at which NO can be converted into NO₂ before the fumes come into contact with the outside environment, by exiting through the evacuation opening 17 and the top slits 7. Through the further top slits 22 ambient-temperature air from the environment outside the heating appliance 1 enters the inside of the body 2 and mixes with the fumes exiting the evacuation opening 17 and cools them before they exit into the outside environment through the top slits 7 and when the temperature conditions of said fumes are such as not to allow the transformation of NO into NO₂.

In this way, it is also possible to ensure that the fumes that exit from the top slits 7 are not at a temperature that is dangerous for persons near said opening, which enables deflecting baffle plates or other protective contrivances to be dispensed with.

The heating appliance 1 can be provided with adjusting means for adjusting the supply of fuel to the burner means 16. Said adjusting means may comprise valves, manual, and/or automatic and/or programmable inserted in the fuel supply pipe.

The heating appliance 1 can also be provided with first safety means to monitor combustion of the fuel and interrupt the fuel supply if operating faults of the burner means 16 arise. Further safety means may also be provided to interrupt the fuel supply if the concentrations of CO in the environment in which the heating appliance is located exceed respective preset maximum values.

FIGS. 5 and 6 show a variation of the apparatus according to the invention.

Said Figures show a heating appliance 100 comprising a body 101 constituting the apparatus according to the invention. The body 101 comprises a front wall 102 and a rear wall 103 connected by side walls 104 and 105. Inside the bottom of the body 101 burner means 106 are arranged in which the combustion of a fuel with which the heating appliance 100 is fed takes place.

At the top of the body 101 there are heat-exchanger means 107 for dissipating, in the outside environment surrounding the appliance 100, part of the heat possessed by the fumes generated by the combustion of said fuel in said burner means 106.

To increase the heat-exchange surface of said heat-exchanger means 107, the top part of the front wall 102 and the top part of said rear wall 103 consist of sections of wall, 111 and 112 respectively, alternately tilted on opposite sides. This allows, maintaining the same height for the appliance 100, to have a greater heat-exchange surface for the heat-exchanger means 107.

The heat-exchanger means 107 are provided at the top with an evacuation opening 108 through which said fumes are ejected into the environment outside the heating appliance. The size of the opening 108 can be varied by choking means 109, for example in the form of a gate valve, that are associated with the evacuation opening 108.

In the bottom part of the front wall 102 of the body 101 there is a window 110 that makes visible from the outside the flames produced by the burner means 106.

The body 101, at the bottom 113, communicates with the outside environment to enable a flow of secondary air towards the burner means 106.

In practice, materials, dimensions and details of execution may be different from, but technically equivalent to those described without departing from the scope of the present invention. 

1. Apparatus for use in combination with a flueless heating appliance for reducing nitrogen dioxide emissions from the flueless heating appliance, said appliance comprising a body, within which burner means arranged that are supplied with a gaseous fuel in the body, supplying means for supplying said burner means with said gaseous fuel, ignition means for causing combustion of said fuel, and evacuation means for discharging into an outside environment fumes produced by the combustion of said fuel, said apparatus comprising heat-exchanger means to be traversed by said fumes and to be placed between said burner means and said evacuation means.
 2. Apparatus according to claim 1, wherein said heat-exchanger means are so sized as to remove heat from said fumes before said fumes reach said evacuation means in a manner to minimize conversion of NO into NO₂ in said fumes.
 3. Apparatus according to claim 2, wherein said heat-exchanger means comprise a front wall, a rear wall and side walls connecting the front and rear walls.
 4. Apparatus according to claim 3, wherein said front wall and rear wall comprise a plurality of wall sections tilted alternately oppositely with respect to a vertical plane.
 5. Apparatus according to claim 4, further comprising respective appendages of respective said side walls, each at a bottom of a respective said side wall, said appendages supporting said burner means.
 6. Apparatus according to claim 5, wherein said evacuation means comprise an evacuation opening in a top zone of said heat-exchanger means.
 7. Apparatus according to claim 6, further comprising means for varying size of said evacuation opening.
 8. Apparatus according to claim 7, wherein said means for varying the size of said evacuation opening comprises choking means.
 9. Apparatus according to claim 8, wherein said choking means re comprise gate-valve means.
 10. Flueless heating appliance, comprising an appliance body, burner means arranged in the body, supplying means for supplying said burner means with gaseous fuel, ignition means for causing combustion of said fuel, evacuation means for discharging into an outside environment fumes produced by the combustion of said fuel, heat-exchanger means adapted to be traversed by said fumes and to be placed between said burner means and said evacuation means.
 11. Heating appliance according to claim 10, wherein said heat-exchanger means are so sized as to remove heat from said fumes before said fumes reach said evacuation means in a manner to minimize conversion of NO into NO₂ in said fumes.
 12. Heating appliance according to claim 11, wherein said heat-exchanger means comprise a front wall, a rear wall and side walls connecting the front and rear walls.
 13. Heating appliance according to claim 12, wherein said front wall and said rear wall comprise a plurality of wall sections tilted alternately oppositely with respect to a vertical plane.
 14. Heating appliance according to claim 13, further comprising respective appendages of respective said side walls each at a bottom of a respective said side wall said appendages supporting said burner means.
 15. Heating appliance according to claim 14, wherein said evacuation means comprise an evacuation opening in a top zone of said heat-exchanger means.
 16. Heating appliance according to claim 15, further comprising means for varying size of said evacuation opening.
 17. Heating appliance according to claim 16, wherein said means for varying the size of said evacuation opening comprises choking means.
 18. Heating appliance according to claim 17, wherein said choking means comprises gate-valve means.
 19. Heating appliance according to claim 15, wherein said body is comprised of a front wall and said evacuation means comprise a plurality of top openings in a top zone of the front wall.
 20. Heating appliance according to claim 19, wherein said top openings comprise slits.
 21. Heating appliance according to claim 19, wherein said top openings are adjacent said evacuation opening of said heat-exchanger means.
 22. Heating appliance according to claim 10, wherein said body is further comprised of a rear wall having a plurality of further top openings in a top zone thereof.
 23. Heating appliance according to claim 22, wherein said further top openings comprise slits.
 24. Heating appliance according to claim 22, wherein said openings in said rear wall substantially face said top openings in said front wall.
 25. Heating appliance according to claim 10, further comprising bottom openings in a bottom zone of said body.
 26. Heating appliance according to claim 25, wherein said bottom openings comprise slits.
 27. Heating appliance according to claim 25, wherein said bottom openings are adjacent said burner means.
 28. Heating appliance according to claim 27, further comprising a still further opening, in a substantially central position of said body, said still further opening being between said top openings and said bottom openings.
 29. Flueless heating appliance, comprising an appliance body burner means arranged in the body, supplying means for supplying said burner means with gaseous fuel, ignition means for causing combustion of said fuel, and evacuation means for discharging into an outside environment fumes produced by the combustion of said fuel, said body comprising heat-exchanger means suitable for receiving said fumes from said burner means and sending them to said evacuation means.
 30. Heating appliance according to claim 29, wherein said heat-exchanger means are so sized as to remove heat from said fumes before said fumes reach said evacuation means in a manner to minimize conversion of NO in said fumes into NO₂.
 31. Heating appliance according to claim 29, wherein said body comprises a front wall, a rear wall and side walls connecting the front and rear walls.
 32. Heating appliance according to claim 31, wherein said heat-exchanger means comprise portions of said front wall and portions of said rear wall, said front wall portions (111) and said rear wall portions being alternately oppositely tilted with respect to a vertical plane.
 33. Heating appliance according to claim 32, wherein said evacuation means comprise an evacuation opening in a top zone of said body.
 34. Heating appliance according to claim 33, further comprising means for varying size of said evacuation opening.
 35. Heating appliance according to claim 34, wherein said means for varying the size of said evacuation opening comprises choking means.
 36. Heating appliance according to claim 35, wherein said choking means comprises gate-valve means.
 37. Heating appliance according to claim 29 further comprising window means in a bottom zone of said front wall.
 38. Heating appliance according to claim 37, wherein said window means are adjacent said burner means.
 39. Heating appliance according to claim 29, wherein a bottom part of said body communicates with the outside environment.
 40. Heating appliance according to claim 10, wherein said burner means comprises burner means suitable for producing a blue Bunsen-type flame.
 41. Method for reducing nitrogen dioxide emissions in a flueless heating appliance, the heating appliance having an opening communicating with an outside environment for discharge of said fumes into said outside environment the method comprising supplying said heating appliance with a gaseous fuel, causing combustion of said gaseous fuel in said heating appliance, sending fumes produced by the combustion of said fuel towards said opening of said heating appliance and removing heat in a from said fumes before they reach said opening in a manner to minimize conversion of NO into NO₂ in said fumes.
 42. Method according to claim 41, wherein said removing comprises passing said fumes across or through heat-exchanger means associated with said heating appliance.
 43. Method according to claim 42, wherein said heat-exchanger means are integrated into said heating appliance.
 44. Heating appliance according to claim 29, wherein said burner means comprises burner suitable for producing a blue Brinsen-type flame. 